Elsa does notice. She notices everything about Anna now, and she can't fully explain why. Perhaps because her apartment suddenly seems so empty; so cold and quiet without Anna there.
She ends up bringing it up to her therapist at their now-twice-weekly sessions, and is given a gentle suggestion to "explore what your friendship meant". When she asks what sort of relationship Elsa had with her, and how it would change or continue after the children were born, Elsa can't find an answer. Her therapist doesn't expect one.
Elsa hadn't really thought about it.